using PuppeteerSharp;
using PuppeteerSharp.BrowserData;

namespace GB5Shared.Export.HybridReport
{
    /// <summary>
    /// Resolves a working Chromium executable for PuppeteerSharp, independent of OS, process working
    /// directory, or deployment folder. Cache path is derived from the running assembly's own directory
    /// (AppContext.BaseDirectory) rather than the process working directory PuppeteerSharp otherwise
    /// assumes — this is what produced the stale "D:\...\BusinessHost\Chrome\Win64-...\chrome.exe not
    /// found" error at the client site. Moves automatically with the build folder on any OS/machine.
    /// </summary>
    public static class ChromiumResolver
    {
        private static readonly SemaphoreSlim _sem = new(1, 1);
        private static string? _cachedExecutablePath;

        public static async Task<string> GetExecutablePathAsync()
        {
            if (_cachedExecutablePath != null && File.Exists(_cachedExecutablePath))
                return _cachedExecutablePath;

            await _sem.WaitAsync().ConfigureAwait(false);
            try
            {
                if (_cachedExecutablePath != null && File.Exists(_cachedExecutablePath))
                    return _cachedExecutablePath;

                var cachePath = Path.Combine(AppContext.BaseDirectory, "ChromiumCache");
                var buildId = Chrome.DefaultBuildId;

                var fetcher = new BrowserFetcher(new BrowserFetcherOptions { Path = cachePath });
                var executablePath = fetcher.GetExecutablePath(buildId);

                // A cache folder can exist with a partial download or an AV-quarantined binary —
                // its presence is not proof the exe is runnable, so always verify the file itself
                // and re-download if it's missing, rather than trusting the cache blindly.
                if (!File.Exists(executablePath))
                {
                    await fetcher.DownloadAsync(buildId).ConfigureAwait(false);
                    executablePath = fetcher.GetExecutablePath(buildId);
                }

                if (!File.Exists(executablePath))
                {
                    throw new FileNotFoundException(
                        $"Chromium executable could not be resolved or downloaded at: {executablePath}. " +
                        $"Verify outbound network access to the Chromium download host and write permission on '{cachePath}'.");
                }

                _cachedExecutablePath = executablePath;
                return executablePath;
            }
            finally
            {
                _sem.Release();
            }
        }
    }
}